The field of the present invention is that of devices used to improve the surface state of a portion of a duct, for example before it is welded to another duct, and in particular the field of manual devices for scraping by rotation about the external surface of a portion of a main feed duct for natural gas before it is connected to a secondary duct, by way of a connecting pipe.
Within the framework of the technique known as the polyethylene technique, the connection of two ducts in which, for example, natural gas circulates, or more precisely the connection of the branch of a connecting pipe to a secondary duct, is effected by the electrical welding of a sleeve around those two tubular parts. In order for welding to be effective, it is preferable to remove the oxidised external surface of the secondary duct and of the branch of the connecting pipe. Therefore, in order to obtain good welding, it is necessary to scrape those parts beforehand. This scraping is generally carried out by means of a scraper of the paint scraper type (wooden handle provided with a transverse metal blade). Scraping with this type of tool is not uniform and the thickness of the material removed is not controlled. The scraped tubular elements have, in particular, a large number of facets. Furthermore, the scraping of the lower portion of the tubular element is not easy and can cause large scratches when the tool slips.
Annular scrapers have also been produced in the past, like that described in EP-A-0 649 694. Owing to the fact that those scrapers are designed for straight-bar tubing, they are not always efficient on ovalised tubes having a given radius of curvature (tubes having a small diameter are delivered in coils). In addition, this tool is very complex to manufacture, and therefore expensive, and must be handled with some care given the number of parts of which it is composed.
In addition, document BE-A-882 419 describes a shaving tool for tubes comprising:
an annular structure having a passage which extends along a principal axis and which is delimited by an internal peripheral surface of the annular structure which is to receive the tube tightly in order to guide it,
a blade secured to the annular structure and having a cutting edge extending beyond the internal peripheral surface to form a projection into the passage.
However, that tool is used basically to dress and bevel the tube by means of two blades arranged perpendicularly, so that the operation for scraping the external surface of the tube can be carried out only over a short distance relative to the end of the tube. Consequently, the tool does not enable the connecting pipe to be welded satisfactorily afterwards.
The solution of the invention which enables the tube to be surface-improved, in other words, which enables its external surface to be scraped over a satisfactory length, consists in that the passage extends right through the annular structure and is partially obstructed by a shoulder defining a region restricting the passage, the shoulder having a height, relative to the internal peripheral surface of the annular structure, which is slightly smaller than that of the projection formed by the cutting edge relative to the internal peripheral surface of the annular structure, so that the shoulder defines an abutment for a non-scraped portion of the tube and permits the passage of a scraped portion of the tube through the restriction.
Thus, a portion of the tube cannot come out of the device again unless all of that portion has been completely surface-improved. In other words, the device itself regulates its advance relative to the tube along the principal axis by not permitting such advance unless scraping of the previously scraped tube portion has been effected completely. Under those conditions, there is no risk of scraping in the shape of a helix while leaving non-scraped tube portions inside the helix.
In addition, the invention proposes that the cutting edge extend axially in the passage, at a distance from the shoulder and at least as far as the limit of the region for restricting the passage, and even partially into that region.
Thus, by maintaining a pushing force on the device combined with a rotating force, the device advances automatically relative to the tube as the scraping thereof progresses, so that continuous surface-improvement is in fact effected.
The invention also proposes that the device advantageously have the following features:
the annular structure is slightly flexible and has a thickness along the principal axis and a width radial to that axis,
the annular structure has a radial slot extending through the entire thickness and the entire width of the annular structure, and
the radial slot is substantially diametrically opposite the blade.
Thus, the annular structure can be deformed in such a manner as to absorb, both when placed in position and during the scraping operation, slight deformation in the diameter of the tube, such as any ovalisation of the tubular element to be scraped. The slot also permits manual modulation of the gripping of the tube and of the thickness of the shaving to some extent.
In order to provide for a good variation in the inside diameter of the passage of the annular structure, the slot of the annular structure extends substantially along the principal axis of the annular structure.
In order to improve the discharge of the shaving, the annular structure preferably has a radial opening which extends over a portion of the annular thickness of the structure and radially over the entire width of the annular structure, the blade extending at least partially into or as an extension of the opening in order to remove the shaving formed during scraping.
In order to make the device easy to produce and light in weight, the invention proposes that the annular structure advantageously be partially hollowed out and produced from plastics material(s).
According to another aspect of the invention, the annular structure has recessed shapes on its external surface which enable the device to be gripped in the hand, in particular concave shapes adapted to receive the thumb and the index finger or the middle finger of a hand. Gripping in the hand is therefore improved in order to cause the device to rotate easily about the tube and to ensure regular circumferential (helical) scraping which is easy to effect because it requires only slight pressure of the user""s fingers.
In order to improve scraping and the formation of the shaving, the blade has, in cross-section, an inwardly curved notch near one end of its cutting edge.
In order to reduce manufacturing costs without reducing the performance of the device, the blade is preferably adhesively bonded in a recess in the annular structure and has a scallop or a protuberance, the shape of which is suitable for fitting a complementary shape formed in the recess of the annular structure, in order to lock the blade laterally in rotation. Thus, while being adhesively bonded, the blade is nonetheless held mechanically by interference in order to prevent any scraping defect caused by inadvertent movement thereof when the device is rotated.
Furthermore, in order to improve the support of the blade and its strength, the invention proposes that:
the blade extend over a specific distance in a recess formed in the annular structure along the principal axis,
the cutting edge of the blade be interrupted by a step, so that the blade projects from the internal peripheral surface of the annular structure only over a portion of said specific distance.
Thus, the length of the blade can be increased for a given edge length, which reduces the stresses exerted on the blade.
The invention and its implementation will become even clearer from the following description which is given with reference to the drawings.